The central goal of this research is to understand the nature of spatial representations, its structure, normal development, and breakdown under conditions of genetic deficit. This goal will be accomplished by studying spatial representations in children and adults with Williams syndrome (WS)~ a rare genetic defect which gives rise to an unusual cognitive profile of severe spatial deficit coupled with relatively spared language. People with WS typically show severe deficits in visual construction tasks. Yet they show spared capacities to recognize objects, process visual motion, and talk about space. This unusual pattern of deficit and sparing suggests the broad hypothesis that dorsal stream functions of the brainmany of them parietal functions- are damaged in Williams syndrome. The pattern also suggests that ventral stream functions, such as object recognition may be spared, and that the combination of damage and sparing leads to the unusual spatial profile of WS. We will test the hypotheses that the WS spatial profile (a) reflects breakdown in multiple dorsal-parietal functions, including visual-spatial attention, updating for action, and imaginal transformations, (b) reflects sparing of object representation, a key ventral stream function, and (c) reflects severe delay or arrest at an early point along the normal developmental trajectory. Experimental probes will test these hypotheses in 4 projects examining visual attention, object representation, visual-manual action, and navigation. This research will shed light on theories of the normal architecture of spatial representation, how it develops in children, and its breakdown during development. The latter holds promise for understanding how to enhance normal spatial representations and build upon deficient ones. The research will have broad impact by increasing our understanding of how spatial systems develop in normal and impaired children. This understanding can afford insights to the applied community which depends on such research to develop interventions.